Method and apparatus for pulverizing materials



Feb. 18, 19 30. w, ARRQWOQD 1,747,922

METHOD AND APPARATUS FOR PULVERIZING' MATERIALS I Filed m 25. 1928 4 Sheets-Sheet 1 j ili n g m am-4 BY M l-J ATTORNEYS 1930- M. w. ARROWOOD IIETHOD AND APPARATUS FOR PULVERIZING IIATERIALS Filed Kay 25. 192 8 4 Sheets-Sheet 2 INVENTOR BY mm? l ATTORNEY 5.

Feb. 18, 1930. v M, w, ARROW-00D 1,747,922

METHOD AND APPARATUS FOR PULVERIZING MATERIALS Filed Nay 25.1928 4 Sheets-Sheet {5 I NVENTOR 74 7 BY v ATTORNEY S Feb. 18, 1930. M W. ARROWQQD 1,747,922

METHOD AND APPARATUS FOR PULVERIZING MATERIALS Filed May 25. 1928 4 SheetsSheet 4 I ENT v z ATT Yy Patented Feb. 18, 1930 (UNITED STATES" PATENT OFFICE l utn'ron w. annowoon, or cinnamon, connnc'rrcu'r METHOD AND APPARATUS FOR PULVERIZIlNG MATERIALS My invention relates to apparatus for andmethod of producing pulverized or powdered materials. The invention is more particufiers in conjunction with or as supplemental to such devices. This has resulted in apparatus of cumbersome or comphcated construction, and usually results in melnnency of operation. produced by undue' limitations in capacity of output, and other disadvantages well recognizedto those skilled in-the art. In some of the prior devicesthe mate- .rial is progressively ground in a plurality of compartments, by the use of freely movable crushing masses, suchas steel balls or bars, pebbles, etc., to produce progressively increasing fineness; and in others, where one stage of grinding is used, the ground material is classified, as by air classifiers, and the too coarse material returned to the machine for further grindlng; while some. prior machlnes use a combination of these principles. It has also been the custom to use a plurality of 'sizes 1 of steel balls as crushing implements, varying in size'from those of sufficient size and weight to crush large lumps to smaller ones for finer crushing. These larger balls consume valuable space thereby reducing the capacity for material to be ground and reducing the total weight ofballs' in the mill.

7 Experiments have shown that .if airis passed through a ball mill interiorly. of the grinding drum that the capacity is increased; 1

but in such cases subsequent classification has been found necessary rial of the desired fineness;

taken at 7-7 of Fig. 5,

v Application filed Hay 25, 1928. Serial No. 280,403.

in conjunction therewith.

An object of the present invention is to obviate these and other disadvantages; and to thereby provide a method of efliciently and rapidly initially producing powdered mateand apparatus which is simple, relatively inexpensive, durable and of relatively small dimensions for the effective carrying out of the method.

The invention consists in the method herein described and in the novel features, arrangement, construction and combination of parts of the apparatus and means hereinafter described in accordance with certain preferred embodiments thereof, and the invention will be more particularly pointed out in the appended claims.

Further objects of the invention will more fully appear from the following description taken in connection with the accompanying drawings illustrating by way of example the preferred embodiment of the apparatus used in carrying out the method.

In the accompanying drawings:

Fig.- 1 is a plan View of my device with the air blower, outlet pipe and material feed hopper omitted for clearness.

FFig. 2 is an end elevation of the device of F Fig. 3 is a side elevation of the device of ig. 1, I

F Fig. 4 is an end elevation of the device of Fig. 5 is a longitudinal section in elevation, taken at 5-5 of Fig. 1,

Fig. 6 is a transverse section inelevation, taken at 66 of Fig. 5,

Fig. 7 is a transverse section in elevation,

Fig. 8 is an enlarged sectional view of the clamping ring details,

Fig. 9 is an enlarged view of a grid bar segmental unit, and

Fig. 10 is a fragmental sectional detail of a modification of the device of Fig. 1 showing an adaptation of the same to central feeding. A brief general description of the present preferred form of the apparatus will first be given, in order to facilitate an understanding of the more detailed description to follow.

In general the machine comprises a rotatable grinding chamber or drum which in ts preferred. form is comprised. of a grid shell in the general type of a squirrel cage with the grid bars standing axially of the drum in substantially parallel spaced relation, the spaces being about 1/50 of an inch wide. This grinding chamber is adapted to contain lump material ofa suitable size and a plurality of grindin masses such as balls or steel bars, rods, etc. ubstantially the entire area of the drum erinhery therefore presents a sieve through which the powdered material may pass when ground to a size of the general order of the resultant pulverization desired. This grid drum is enclosed within a suitable casing which is adapted to receive tain definite range,

the powdered material resulting from the grinding operation. The casing is provided with suitably "formed intake and outlet orifices and the intake orifice is connected to a suitable air pressure source, such as a fan or Root blower to force air into the casing. The speed of rotation of the grinding drum is such that, with the construction employed,

the combined charge of lump material and crushing masses will be given a cascade efiect to thereby pulverize the material. The area and shape, of the air inlet orifice-is such, in proportion to the area within the casing, that the velocity of air flowingwithin the casing will be sufficient only to entrain and pick up powdered material of the size ultimately desired; the fluid mass of air and entrained powdered material is then passed outwardly through the outlet orifice and taken to the source of supply or to a suitable collecting chamber. In the preferred embodiment the lump material is introduced directly into the casing exteriorly of the grid shell grinding I drum and is there initially broken and simultaneously moved toward one end of the cas ing by spiral means on the exterior of the rid drum, from where it is moved inwardly radially by volute' veins and introduced into an axial opening'at the adjacent end of the drum; such particles as have passed through the shell and "are of a size too'large to be removed by the current of air, are likewise moved by the spiral veins and lifted by the.

volute veins back into the'r pulverization.

I have further found that the-greatest efficiency and resultant economy is obtained by operating upon lump material within a ceras will be more specifically pointed out following; and that due to 111 method of removing the pulverant from .vhthin outwardly not only is the attrition imthe grid shell for furto, and the gear proved butmore material may be handled over a given period of time than was poss'ible in the usual method of grinding. thermore, material once delivered from the grinding pperation, by the air current as employed, needs nofurther classification and is ready for consumption.

Referring more specifically to Figs. 1 to 4;, inclusive 2 the base of the apparatus will be designated in its entirety as 1. Asuitably formed casing 2, which is pr eferably made in sections to facilitate its manufacture-,is suitably attached to the base land is provided with a longitudinal opening 3 for the admission of lump material. A. suitably formed inlet orifice member 1 is attached to the casing 2 and the orifice therein is in communication with a suitable supply. of air under pressure, such for example as by being attached to a fan blower (not shown) capable of delivering a predeterminedfsupply of air. A suitably formed outlet orifice member 5 is attachedtothecasing,oppositely disposed from the orifice 4 both laterally and longitudinally, sothat the orifices are positioned on diagonally opposite sides of the casing 2. The casing and orifice members are so formed and positionedthatthe air current passing intothe casing will flow circumferentially downward and axially thereof, passing out at a point diagonally opposite to its point of entry. I 1 4 g The predetermined supply of air under pressure is expanded within said casing,.due to, the increasedarea of fiow stream, resulting in a corresponding decrease in velocity to such a degree that only a pulverized material ofthe desired fineness will be entrained in and removed by said air current.

The sieve-like crushing drum chamber will be designated in its entirety as 6 (Fig. 5). This drum is supported by the drum. ends 1y. with axles'9 and 10 passing outwardly through respectively.v opposite ends of the casing 2 and having substantially sealed con-' tact with the casing by means of the sealing Fur, Q

7 and 8 which are provided respective- A means 11 and 12. The axles 9 and 10 are 1 caps 15 and 16; thejournals so formed being suitably lubricated such for example as by lubricating rings 17. The axle 10 projects outwardly beyondthe journal support 1&- and carrles a gear wheel 18 suitably keyed thereand the projecting portion of the axle 10 18 carried thereon are additionally supported on suitable. journals formed in the gear wheel housing 19 which is sup ported from the base 1. The gear wheel 18 (Fig. 2) is in mesh with pinion gear 20 carr1edon the shaft 21, also journaled in the housing 19, and carrying the gear 22 which s thereby connected to the pinion 20 for rotation therewith. The gear 22 is in mesh 7 with ,a

pinion gear 23, suitably attached to the drive shaft 24, which is journaled in the housing 19 and which is connected to the drive shaft of a motor 25, by suitable means, such as the universal joint 26, or other'suitable flexible coupling; theabove gear train and motor serving to rotate the drum 6 at a suitable speed, such speed for the present %mll)&diment being preferably about '30 R.

The grinding chamber drum 6 has been found to give the most satisfactory results when constructed of grid bars 27 as shown in Fig. 9. In the present embodiment the grid drum is about 5 internal diameter and the. gridbars'27 are approximately 1 in cross section, with the greater dimension extending substantially radially. The grid bars are assembled in units for purposes of. manufacture, in the present embodiment 6 of such unitsbeing employed. The unit grid bar assembly is clearly shown in Fig. 9. from which it will be seen that the grid bars are attached together by means of-tie rods 28 passing. through holes in the grid bars, the grid bars alternating with spacing washers. of approximately 1/56" thickness. The grid bar units so assembled are in the form of segments (j ormedalong an arc in conformity with the size of drum desired. .A plurality of tie rods 28 are used to attach the grid bars together m such a construction. ,Each grid section (F ig. 9) includes a relatively heavy bar 30 5;" which is provided with an outward beveled face '31, forthe purpose tobe described following. v

The grid drumheads proper, which together with the grid segments form the grid drum, will be designated as 32 and 33 (Fig.

5). Each head carries an inwardly extendingfannular flange (Fig. 8) 34 on which the grid bars 27 are supported. The drum heads 32 and 33 areslotted radially at intervals 1' spaced circumferentially distances approxi-' mately equal to the width of. the grid segments providing slots 35 (Fig. 5). Liftingand clamping bars 36 (Figs. 5 and 9) are provided with one side beveled corresponding to the beveled face 31 of the bars 30 and are provided adjacenttheirouter ends with undercut rectangular portions 37 and at their ends with threaded stud projections 38.

These bars are of a width in a radial direction substantially greater than the grid bars 27, andtheir undercutend's 37 are adapted to fit into the radial slots 35 formed in the drum heads 32 and 33 in such; position that the inner faces of thebars 36 will extend inwardly radially a substantial distance'beyond the mner edge of the bars 27. The grid bar seg- '-ments are'placed' on shoulder 34 between the heads 32 and 33 with lifting and clamping bars 36 alternating therewith, as clearly shown in Figs. 5, 6 and 9, and with'th'e stud ends 38 positioned in radial slots formed in the drum ends 7 and 8. When the parts'are placed in this position clamping ring segments 39 (Figs. 5, 6 and 8) are placed in position as shown and clamp blocks 40 are attached thereagainst by means of studs 41 which are placed in threaded engagement with the drum heads 32 and 33. The adjacent faces of the clamping segments 39 and blocks 40 are cooperatively beveled and the segments 39 are provided with radial slots through which the studs 41 pass. It will therefore be seen that by-tightening up on the studs 41 the clamping ring segments 39 and effectively clamp the drum ends, heads.

and side wall firmly together intoa substantially integral unit.

The drum head 32 is provided with an axial opening 43. (Figs. 5 and 6), and this end of the drum is otherwise closed by the head 32 which forms a circumferential and marginal closure. The opening 43 is provided with an,

inturned radially outwardly flaring annular lip 44 (Fig. 5), which is adapted to retard the passage of material outwardly through this opening. The drum end 7 is provided with a central hub 45 from which veins 46 (Fig. 6) radiate in a general outward direction in the. form of volute veins, which terminate adjacent the outer periphery of the drum end 7, as at 46'. These volute veins '46 act as spacer means between the drum end 7 and the drum head 32; the drum head and end being clampedtogether by suitable means suchas the bolt and lug means 47 (Fig. 6). The drum end 8 and the drum head 33 are similarly spaced apart in clamped and spaced relation by spacer-lug and clamping means, designated as 48 (Figs. 5 and'7).

Spiral veins 49 (Figs. 5 and 7) are attached to the outer periphery of the grid drum 6 m such position that upon rotation of the drum in the direction indicated in Figs.- 6 and 7,.

the materialf resting in the bottom of the casing 2 will be moved toward the right hand end of the casing (with reference to Fig. 5) The'spiral veins 49 are spaced apart circumfe'rentially and are discontinuous in the preferred embodiment; thereby serving as ameans for somewhat further breaking up the lumpmaterial'mass entered into the casing through the opening 3, and further serv- 1n the primary purpose of agitating the ma ss of material theicasmg and diffusing substantially of the same size it in the air current, in order to assist in freeing the particles of'the desired fineness to be entrained in the air flow.

The apparatus is adapted to. be operated under normal feed conditions and also under forced feed conditions. In the'latter event the material. is fed into; the drum at a rate somewhat in'excess of'the passage of powdered material outwardly through the grid bars. Hence for such forced feed conditions I provide a means of egress from the drum by forming an opening (Figs. and 7 in the drum and formation as'the opening 43 in the drum head 32; and its function will be more fully described following. v v

The device herein shown in the preferred embodiment is subject to many modifications. As the principal one of these modifications provision may be made for feeding the material to be ground directly into the drum grinding chamber; and I therefore show a modified structure in Fig. 10 which illustrates the preferred form of adaptation of the apparatus hereinbefore described to thls type of operation. Since other parts of the device already described are substantially identical in this modified structure Fig. 10 shows merely afragmental section In detall, and it is to be understood that the remainder of the machine used in conjunction with the details shown in Fig. 10 are to be identical with those hereinbefore described with such exceptions as are to be more fully pointed out. Correspondingly, similar parts in Fig. 10 will bear corresponding reference characters as employed inthe foregoing embodiment with the addition of the prlme suffix (1'1). In connection with t e inlet opening 3 is entirely closed.-

the journal support 13 is adapted to support the axle 9 of the drum end .7' the axle 9 preferably being relatively larger than the axle 9 and being provided with 1 an axle bore 51. The axle 9' carries a gear feed housing 61, which 52 suitably attached thereto as by a key. The

gear 52 is in mesh with the gear 53 suitably attached to a shaft 54:, which is supported by suitable journals such as 55, attached to the journal support 13', and 56, which is attached to a supplemental support 57 The shaft 54 projects outwardly beyond its journal 56 and carries attached on its outer end a gear 58 which is in mesh with a gear 59 journaled on a screw shaft 60. The screw shaft 60 is journaled adjacent the gear 59 in the wall of a is suitably attached and carried by the support 57. The feed housing 61 is provided with a flange which substantially Surrounds the hollow axle 9' in such a manner as 'to prevent any undue leakage of material between the housing and axle end. The feed housing 61- may be to be pulverized.

head 33. This .openmg' is 1 ment.

this embodiment Referring more-particularly to Fig. 10 v Within the'igrid drum formed'as a part V attachment to the feed supply of material The screw shaft carries a of or may be adapted for spiral screw 62 which passes through the bore 51 and that portion of the feed housing 61 in register therewith, and is adapted upon rotation to feed material from the feed housing 61 through the bore drum. through the opening 43'.

51 and into the grid It is to be understood that the drum end- 7 is provided with volute spiral veins such as described in connection with the. drum end 7, and that the general formation and configurationof the drum end 7 and drum head 32 are in accordance with the detailed description hereinbefore givenin connection with the corresponding parts of the The apparatus above described is ada ted to be used in connection with suita le pulverized into lumps of suitable size, such for example as size; it being understood of course that while the majority of the charge of lump material so broken is in the nature of the size above indicated, nevertheless some of the charge will comprisea small percentage of lumps of other sizes. In using the apparatus in connection with such crushing or breaking first embodi-" mechanism for breaking the material to be lumps of about 3" to 1 in means, the crusher or breaker is mounted on the top of easing 2 with its outlet in register with the opening 3 (Figs. 1 and 4). However, it is to be understood that the use of the machine is not to be'limited in this respect, but is equally well adapted to receive its charge of material from any suitable source of supply as by being connected with the outlet. of a supply vent, all of which will be well understood by those ski'lled in the art.

The mechanical masses which are placed 6 and which are used in combination with the apparatus described above for assisting in the attrition of thevlump material may be in the form of one or more bars, or rods, or balls of steel, or may be formed of any suitable material, less frang ible than the material to be pulverized. I Y

prefer to use steel balls as the mechanical masses, since I have found these well adapted for use in combination with the preferred form of my apparatus. I have found by experiment that in the preferred form of apparatus, balls of about 1 ..diameter (weighing about lb. each) are well adapted to accomplish the work desired inthe preferred method of carrying out my'invention. Due to the improved structure of my apparatus, and the method of carrying out my invention, I have found that these balls may all be of about this dimension as opposed to the usual prior practice of using balls of varying sizes, but this'is merely one phase of the invention.

In the prior devices of this general type,

: i'i -efball mills, each cubic foot of grinding charge (which comprises material and breakingjmasses) comprised about 320 lbs. of

breaking-masses (such a's balls) and 25 lbs. of lump material. I have found that in carrying out my process the coal contained per cubic foot of charge may be increased by reducing the crushing "masses by about A or thereby permitting a corresponding increase in volumetric content of material to be pulverized; This increase is due to the reduction in gross weight or size of crushing means, such for example as the balls which act as crushing masses in the present preferred embodiment. gross weight of crushing means directly affectstheincrease in the coal handled per cubic foot, due to the'greater space available -which is broughtabout by the above-noted reduction in the volumetric content occupied by the crushin means; and this increase is further due in irectly to the removal of the pulverized material from the zone of pulverization, in a manner to be particularly pointed out following, which permits ,the coal to be ground toreplace the space otherwise occupied by the powdered material. The efficiency of the mill is also increased=,by removing the powdered material from the zone-of pulverization, thereby allowing the mechanical crushing means to act directly upon'the material to'be pulverized, and al o resultin in decreasing the circulating load of the milfi i. e. causing a very large percent of the material introduced into the mill to he pulyer izedduring its passage through one cycle of operation of the mill,

Operation A suitable charge of the steel balls is introduced into theinteriorbfthe griddrum 6 and-thev driving mechanism is put into operation, to therebyrotate the grid. shell at a speed of about R. P. M. in the present embodiment. Lump material of suitable size is introduced into opening 3 and passes I around theperiphery of the grid drum 6 into the bottom'of casing 2, as more particularly indicated in Fig. 7. A suitable predetermined supply of air under pressureis introduced into' orifice member-'4, from-a fan blower or,in any other suitable manner. The

drum 6 is nowrotatlng as indicated in Figs.

6 and 7, causing the discontinuous spiral veins 49 to advance the lump material toward the drum end '7. During this introduction and advancement period-any material particles, such as coal dustin the event that coal is being pulverized, of the predetermined.

desired size are entrained in the air current whichv is passing inwardly through orifice 4 and outwardly through orifice 5 in a general spiral directionand are "carried-from the casing suspended in the current of air in what might be termed a fluid mass; the powdered In this reduction the coal so removed being thus transferred to any desired point. The lump material which has been progressively moved to the drum end 7 is lifted by the volute veins 46 and is moved radially inwardly, being deflected about the cone hub 45 (Fig. 5) through the opening 43, and into the grid drum. The flow of lump material introduced into opening 3 is so controlled and proportioned, with respect to the capacity of the machine, that during the operation of the machine the grinding charge within the grid shell, i. e., lump material and balls, consumes approximately 40% to 5 0% of the volumetric space of the pulverized within the grid drum 6 passesoutwardly through the grid shell, between the grid bars 27. Most of such powdered material which passes through the grid bars is of the desired fineness and all of such material is of the order of the fineness ultimately desired. By this I mean that the material capable of passage through the grid shell is substantially of the size desired and in any event will only have to be slightly altered in size inthe manner to be described following.

The discontinuous spiral veins 49 serve the additional purpose of agitating the material in the bottom of casing 2 to thereby allow .the powdered material of suitable fineness to be pickedup by the air current. Such material remaining in the casing and not entrained in the air flow is progressively .moved by discontinuous veins 49 as above described and is introduced into the grid shell. ation in general is as follows. Lump-material having been introduced into the casing 2 and having been inserted in the-grid drum 6 the powdered material passes through the grid bars 27 and such of it as is of the desired degree of-.fineness is drawn away by being entrained in the flowing air; while such of it as is still too coarse to be so re-' In other words, the cycle of opera moved is pushed by the spiral veins 49, to-' v gether with the. lump material, back'into the feed head of the machine and is movedby the volute veins 46 through the center opening of the grid drum 6 .into the grid drum. In this manner the internal circulating load is increased and the fines are still more rapidlyremoved, slnce a cons derable attached to the outside of the grid drum, so that any dust contained has full opportunity to be picked up and carried away by the air current.

In the above oper tion as specifically described, the opening 50 in the drum 33 is not essential. However, in instances where forced fwd is desired, to somewhat increase the capacity of the machine, the opening 50 is necessary, as will not; be more particularly pointed out. Where forced feed isuti lized, the input of the material is increased slightly in excess of the output of the machine as above described, and the material being fed into the drum head 32 causes a progressive axial movement of the material in grid shell 6 from where a part of the materia is passed out through the drum head 33. This axial circulation of the material through the drum increases the agitation of the material, and allows a greater percentage of the particlesof the desired fineness to be entrained in the air current.

My invention is also applicable to an axial feed, and in order that such adaptation may be clearly understood, I have shown in Fig.

'10 a modification adapting such apparatus to this use. The operation of the modification is in general quite similar to that above described, except that tially introduced into the machine is introduced through the feed casing 61. In connection with this axial feed modification, it might'be pointed out that since the hollow drum axle 9 is rotating, it is only necessary to rotate the feed screw 62 very slowly in the opposite direction in order to initially pick up the coal from the housing 61;. the effective relative speed of rotation of the feed screw 62 in the axle 9 being equal to the sum of the rotative speeds of the axle 9 and .the feed screw 62.

Although my invention has been found to be extremely useful in connection with pulverizing coal for fuel burning purposes, nevertheless it should be borne in mind that there are perhaps in 200 commercial products which may be pulverized according to my invention with equally satisfactory results. By way of example of one of such other materials might be mentioned Portland cement as one which may be efficiently and admirably handled according to my invention. It is therefore to be understood that the invention is not to be limited to its use in connection with the pulverization or reduction in fineness of any particular material.

It is a well known fact that in passing fine powder through fine slots or cracks it often tends to become'packed therein and thus clogs the'openings and restricts the free flow of the powdered material. Due to the circulat tion of gravity and the lump material ini-- the neighborhood of ing air around and about the grid drum there results a definite infiltration of air in the slots between the grid bars, which keeps the'material from compacting in the slots; and in effect forms a partial'suspension of the dust in such infiltrated air, permitting its ready passage through centrifugal force. Having thus described my invention with particularity with reference to the preferred method of carrying out'the same and in connection with the preferred apparatus for carryingout the same, and having referred the slots under the acv to some of the possible modifications thereof,,it will be obvious to those skilled in the art, after understanding my invention, that other changes and modifications may be made therein without departing from the spirit and scope of my invention, and I aim in the appended claims to cover such changes and modifications as are within the scope of the invention.

1 What I claim'as new' and desire to secure by Letters Patent is 1. The method of removing material from a pulverizer, which comprises imparting inter-lump attrition to a charge composed of frangible lump material and masses of relatively less frangible material during agitation, removing radially outwardly by gravity powdered frangible material so produced from the zone of pulverization, and further removing said powdered rent of air passing externally spirally of said zone of pulverization substantially throughout the axial length of said zone.

material with a cur- 2. In pulverizlng apparatus, the combination of a rotatable sieve drum receptacle adapted to contain a material and masses of less frang1ble .material and provided with an end aperture, a casing'substantially enclosing said drum an provided with an aperture for the'admission of lump material thereto, and means for transferring said material from said .casing into said drum. Y Y

3. In pulverizing apparatus, the combination of a rotatable sieve drum receptacle adapted to contain a charge of frangible lump material and masses of less frangible material and provided with an axial apertur'e,:a casing substantially enclosing said drunii and provided with an aperture for the admission of lump material thereto and volute means for transferring said material from said casing into said drum. 7 4;. In pulverizing apparatus, the combinae charge of frangible lump tion of a rotatable sieve drum receptacle stantially enclosing said drum and 1 26. provided with an axial aperture, a

' I provided with an aperture for the admission 1o.

and means at said end fortransferring said material into said drum.

5. [In pulverizing apparatus, the combination of a rotatable sieve drum receptacle adapted to contain a charge of frangible lump material and masses of less franglble material and provided with casing substantially; enclosing said drum and of lump material thereto, means rotatable with said drum for feeding-said material toward one end of said casing, and means at said end for transferring said material into said drum.

casing substantially enclosing said drum and provided with an aperture for the admission oflump material thereto, spiral veins carried exteriorly-of and. rotatable with said drum for moving said lump material toward .one' end ofsai'd casing, and a plurality of rotat able volute 'veins so positioned and construct ed as to further move said. material from said end of said casing into said drum.

7 i In pulverizingapparatus, the combination of a rotatable sieve drum receptacle adapted to contain a charge of fran ible lump material and masses of less frangible material" and provided with an axial aperture, a

provided with an aperture for the admission of lump material thereto, discontinuous spiral veins carried exteriorly of and rotatable I with said drum for moving said lump mate-- rial toward one end of said casing'and for further reducing the size ofsaid lump mate rial, and means for further moving sa1d material from said end of said easing into said drum. l I 8. In pulverizing apparatus, the combination of a rotatable sieve drum receptacle adapted to contain a charge of frangible lump 7 material and masses of less franglble mate- .rial and provided with an end aperture, a

casing substantially enclosing said drum and provided with an aperture for the admission of lump material thereto and apertures for the respective admission and emission of air thereto and therefrom,,said air aperturesbeing positioned at diagonally opposite Slat 5S of said drum and being so formed that a1r passing therethrough will enter sa1d casing substantially tangentially of sa1d drum at one end thereof and will leave said casing "a direction substantially tangentially of sa1d drum adjacent the opposite axial end of said drum, and means for delivering said lump material into said-drum.

9. In a-pulverizer of the character described, a rotatable sieve drum com rising axially extending substantially paral el ciran axial aperture, a

apparatus, the combinaand having air inlet and outlet apertures for i the passage of a current of air respectively into and out of said casing for conveying said powdered material therefrom.

10. In a pulverizer of the character. described, a rotatable sieve drum comprising P axially extending substantially parallel circumferentially spaced grid bars the widthof Whose axially extending spaces thus formed is of the order of the ultimate degree of fineness desired in the .Whereby when said powdered material has reached the proper degree of fineness it will pass through said spaces under gravitational and centrifugal action, a casing substantiallyenclosing said drum for receiving said powdered material and having air inlet and outlet apertures for the passage of a current of air respectively into and out of said casing for conveying said powdered material therefrom, said casing also having an aperture for the admission of lump material to be pulverized, and means for moving said lump material from said casinginto said drum.

11. In pulverizing apparatus, the combination of a stationary casing having apertures for thevadinission of lump material and for the admission and emission of moving .air, a rotatable container and sifter drum within said'casing provided with circumferential marginal end closures, and means for container, and means comprising means for marginal end closures,

pulverized material, 4

supplying air under pressure and suitablv formed and positioned inlet and outlet orifices associated with said casing for removing said powder in the form of a fluid mass.

- 13. In pulverizing apparatus, the combination of a rotatable grid drum, means for introducing material axially within said drum during rotation thereof, circumferential openings in said drum for discharging pulverized material radially outwardly and means substantially enclosing said drum for suitable supply of moving air .to a path sub- .stantially circumferentially externally of said drum, said enclosing means being provided with diagonally opposed inlet and out- P let openings to thereby cause said air current to simultaneously move axially of said drum.

15. In pulverizing apparatus, the combination of a rotatable grid drum, means for introducing material axially within said drum during rotation thereof, means substantially enclosing said drum for confining a suitable supply of moving air to a pathsubstantially oircumferentia-lly externally of said drum, and conveyor means within said enclosing means for moving. material into said drum.

I trition, removing a 16. A method of pulverizing frangible material comprising rotating a mass of the material and pulverizing it by inter-lump atthe pulverizing material of'less than a predetermined degree of fineness radially outwardly from said revolving mass, moving a column of airthrough the pulverized material thus removed and en-.

' training into said air pulverized material of a predetermined lesser degree of fineness, and returning to said mass for further attrition pulverized material previously removed but P of greater than said lesser degreeof fineness. 1 17 A methodof pulverizing frangible material comprisin rotating a mass of frangible material and pu verizing it by attrition, separating from said mass pulverized materlal of less than a predetermined'degree of fineness, mixing the separated pulverized material intoa stream of air and entraining thereinto material smaller than a second lesser predetermined degree offfineness, removing the air and entrained material, and

returning to said mass previously separated material of larger than, said second predetermined degree of fineness; 18. A method of pulverizing frangible material comprising rotating a mass of frangible material and pulverizing it by attrition, separating from said mass pulverized material of less than a predetermined degree of'fineness, mixing the separated pulverized material into a stream of air and entraining thereinto material smaller than a second lesser predetermined'degree of fineness, re-- moving the air and entrained material, and returning to said mass previously separated material of, larger than said second predeconcentrically within the other, pulverizing the material in both said masses by attrition, removing pulverized material of less than a redetermined fineness from the inner mass centrifugally into said second mass and removing from said second mass by an air thesame in steam, material of less than predetermined fineness by entrainment into said-air.

20. A method of pulverizing frangible material comprising forming two rotating masses of said material, one being positioned concentrically within the other, pulverizing the material inboth said masses by attrition, removing pulverized material of less than a predetermined fineness from the inner mass centrifugally into said second mass and removing from said second mass by an air stream material of less than a predetermined fineness by entrainment into said air,and con ducting portions of said outer mass into said inner mass for further attrition thereof.

21. A method of pulverizing frangible material comprising forming two rotating masses 'of-said material, one being positioned concentrically within the other, pulverizing the material in both said masses by attrition, removing pulverized material of less than a redetermined fineness from the inner mass centrifugally into said second mass and removing from said second mass by an air stream material of less than a predetermined fineness by entrainment into said air, conducting portions of said outermass into said inner mass for further attrition thereof, and feeding fresh sup lies of unpulverized material to one of sai masses.

22, A method of pulverizing frangible material comprising rotating a mass of the material and pulverizing it by attrition, remov ing pulverized material of less than a predetermined fineness from said mass centrif ugally only as vand when formed, discharging said removed pulverized material-into a'stream of air, propelling said air through an outlet and entraining thereinto pulverized material of less thana predetermined degree .of fineness, and returning to saidmass from ness, projecting said removed material into an air stream, propelling said air in a general direction past one end of said revolving mass and entraining thereinto pulverized material 5 of less than a predetermined fineness, and moving'in a general direction toward the other end of said revolving mass through said air stream pulverized material too large to be entrained by the air and returning the 10 last said material into said mass for further attrition' v In testimony whereof I have signed my name to this specification.

MILTON W. ARROWOOD 15 

